Test arrangement and method for testing breakage and mechanical properties of rock particles

ABSTRACT

The invention relates to a test arrangement for testing breakage and mechanical properties of rock particles. Test arrangement comprises: a support (1, 2); two counter-rotatable crushing wheels (3, 3′) supported on the sup-port (1, 2); and a drive arrangement (M1, M2) for rotating the crushing wheels (3, 3′), said crushing wheels (3, 3′) facing each other and defining therebetween an in-put gap (G) for the rock particles, said wheels being arranged to break the rock particles (RP) to smaller daughter particles (DP), wherein the test arrangement is arranged to receive only one rock particle at a time to be inputted to the input gap for breakage testing, an energy measurement arrangement (5, 5′) arranged to measure in-formation relating to energy absorbed by the rock particles (RP) during the breakage, a processor (PR) coupled to the energy measurement arrangement and arranged to receive, as inputs, at least one degree of breakage of the rock particles as a result of the breakage and the corresponding breakage energies absorbed by the rock particles (RP) during the breakage, to determine a correlation between the degree of breakage and the breakage energies, and to output the correlation.

BACKGROUND

Orebodies are intrinsically variable in composition and physicalproperties by virtue of their heterogeneous nature. Few orebodiesconsist of one single lithology or any other geological classification(ore types). This variability is usually evident from orebodycharacterization programs by showing the spatial distribution of theseproperties. Orebody complexity is well recognized; However, the designof most processing plants is still performed using fixed or discretevalues of the orebody properties as input parameters. Designing aprocess plant has many conventions, and one of these is that selectingthe 80^(th) percentile value of a key measurement; where the 80^(th)percentile is determined based on the availability and representation ofthe test sample in the LOM.

Mining companies tend to invest more in understanding resources than inunderstanding metallurgy, of which comminution testing is a keycomponent. If the test work program is not adequately executed andinterpreted, there are risks of establishing wrong design criteria andcompromising the final design. One consequence of this is that severalprojects have underperformed (mainly throughput) and have resorted tospending additional capital to mitigate the problem (e.g. secondarycrushing, high-intensity blasting and/or barren pebble rejection).Another consequence is that some financiers are expressing lessconfidence in the engineer's ability to predict the performance ofgrinding circuits, and this has impacted on the ability of companies toobtain funding.

Comminution tests are a critical element in the proper design of orebeneficiation plants. Traditionally, test work has been conducted with afew representative reference samples. For geometallurgical modelling,the entire ore body is explored based on drill-core samples tounderstand the variability within the resource and to establish spatialgeometallurgical domains that show the differential response to mineralprocessing. Setting up a geometallurgical program for an ore depositrequires extensive test work. Methods for testing the comminutionbehaviour must therefore be more efficient in terms of time and cost,but also with respect to sample requirements. The integration of thetest method into the geometallurgical modelling framework is alsoimportant.

Geometallurgical mapping/modelling is needed for finding out theproperties of ore bodies or other rock bodies or particles thereof. Forthis purpose, rock particles are subjected to breakage characterizationtest.

Breakage characterization test can give useful information regardingfeatures of the rock bodies for better designing the process equipmentsuch as comminution devices of the mining industry processing plant.Deeper knowledge regarding rock breakage properties would be highlyadvantageous because more than 50% of the energy consumed in mining isconsumed in comminution, compared to only 10% in excavation.

Different techniques have been developed to assess the breakagecharacteristics of rocks or orebodies and to generate the parameters formodelling. A drop-weight test is an example of a conventional method forassessing the breakage characteristics of a single piece of rock or anorebody. A conventional drop-weight test (DWT) ore breakage devicerequires laborious manual procedures and fixed energy levels. In such adrop-weight test, either an orebody under examination or a weightarranged to drop on the orebody is raised to a determined height andthen allowed to drop, thus causing breakage of the orebody (if theheight is sufficient to cause the breakage). The breakage energy levelis determined by the height. Use of such fixed energy levels is alsoinaccurate.

BRIEF DESCRIPTION

An object of the present invention is to provide a test arrangement tosolve or to alleviate the above disadvantages. The purpose of theinvention is to enable fast and low-cost single particle breakagetesting in a wide range of rock sizes. The characterization intends tomeasure the compressive strength and the actual total energy absorbed byeach particle. The absorbed energy is then related to the progenyproduced from the parent particle.

The objects of the invention are achieved by a test arrangement andmethod which are characterized by what is stated in the independentclaim. The preferred embodiments of the invention are disclosed in thedependent claims.

An advantage of the disclosed test arrangement and method is that it isable to accurately produce extensive rock compressive strength andsingle particle breakage characterization data, while still being ableto remain fast and suitable for low-cost online testing.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail bymeans of preferred embodiments with reference to the accompanyingdrawings, in which:

FIG. 1 shows test arrangement

FIG. 2 shows the relationship between the degree of breakage parameter,t₁₀ (% smaller than 1/10^(th) of the particle original size) and thespecific breakage energy, Ecs (kWh/t)

FIG. 3 illustrates a flow diagram of a process for measuring the appliedforce and energy absorbed by each particle during breakage; and

FIG. 4 illustrates a force measurement signal.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a test arrangement TA for assessingthe breakage properties of rock particles RP, said test arrangementcomprising a support 1, 2 and two counter-rotatable crushing wheels 3,3′ supported on the support 1, 2. Support 1 for first wheel 3 can beseen as a rigid frame and support 2 for second wheel 3′ is a movablevertical beam or other support 2 that can be moved, thanks to adjustmentmechanism 6 having a slot 6A and element 6B such as bolt, at the supportframe 1 and an element such as nut 9 (on the bolt 6A) arranged to presshorizontally movable support beam 2 against frame 1. Support beam 2 withrelated second wheel 3′can be horizontally moved in relation to support1 and in relation to first wheel 3. This second support 2 supporting thesecond wheel 3′ is movable so that the width of the input gap G betweenthe wheels 3, 3′can be adjusted. Similar or different adjustmentmechanism 8 can also be at the lower end of the support beam 2.

The adjustment mechanism 6 or 8 can also been seen as a hinge or a partof the hinge, intended for protection purposes. Relating to that, if theforce caused by the crushed particle exceeds the friction produced bypressing the support beam 2 against the support frame 1, then thesupport beam 2 may rotate around the part 8 (adjustment mechanism/hinge)to allow the second wheel 3′ to escape and relieve the force, as aprotection mechanism against excessive loading.

During the operation of the arrangement, the gap adjustment mechanism islocked and the upper and lower ends of the support beam 2 do not move.End of the support beam 2 is pressed/clamped against the support frame 1so that the friction between the parts prevents the support beam 2(carrying the second wheel 3′) from moving.

Individual rock particles RP enter the gap G between the parallelcounter rotating wheels 3, 3′ one-at-a-time. The arrangement comprisesforce measurement arrangement 7, 7′ for measuring the breakage force ofeach rock particle RP. Force is measured from the forceful bending(caused by rock particle RP between the wheels 3, 3′) of the supportbeam 2, support beam 2 is locked to its place at both ends of thesupport beam 2.

One or both ends of the beam 2 could be hinged against the frame 1 afterthe gap adjustment is fixed in place. Both the rotation and thehorizontal movement of the end of the support beam 2 in relation to thesupport frame changes the bending behaviour of the beam 2, this whichcan be taken into account by software calibration.

In an embodiment, the force measurement arrangement 7, 7′comprises oneor more strain gauges, sensing the bending deformation of the verticalsupport beam 2. The support beam 2 (carrying the second wheel 3′) andthe related strain gauges together form a load cell. In an embodimentand as an example only, a suitable strain gauge can be KyowaKFG-5-120-C1-11L3M3R. Other means of measuring the bending of thesupport beam 2 are possible, too. The force measurement arrangement 7,7′is to measure information relating to the rock particle compressivestrength, said force measurement arrangement 7, 7′ being coupled vialines 17, 17′ to a processor PR, said processor PR being arranged tocalculate the breakage force applied to each rock particle RP over time.

Crushing wheels 3, 3′ i.e. comminution wheels i.e. rotatable crushingelements can be narrow wheels, having narrow axial width of for example25-50 mm, and diameter of for example 20-80 cm. One possible materialfor wheels 3, 3′ is metal, such as hardened steel. An example of theweight of each wheel 3, 3′ is 10-100 kg, such as 40-60 kg, this dependson the required maximum available energy.

Additionally, test arrangement TA comprises a drive arrangement M1, M2for rotating the crushing wheels. Drive arrangement can be integratedgearless electric motors M1, M2. As an example only, suitable powerrating for electric motors is 50-100 W.

Crushing wheels 3, 3′ are facing each other and they define therebetweenan input gap G for the rock particles RP, said wheels 3, 3′ beingarranged to crush/comminute rock particles to smaller daughter particlesDP (progeny). Test arrangement is arranged to receive only one rockparticle at a time to be inputted to the input gap between the wheels 3,3′. This may be arranged by controlling a feed mechanism such that onlyone rock particle enters the input gap at a time. The applied force forbreakage and the energy absorbed by each particle is measured by themethods presented below.

Width of the gap G is adjusted to be less than the size (minimumdiameter) of the inputted rock particle RP. In an example, width of thegap G is percentage (25 to 75%) of the average particle size (diameter).Particle size can range from 8 mm to 50 mm.

The test arrangement TA further comprises an energy measurementarrangement 5, 5′ for determining of the energy absorbed by each rockparticles during breakage, said energy measurement arrangement 5, 5′being coupled to said processor PR via lines 15, 15′, said processor PRbeing arranged to calculate energy absorbed by each rock particle RPduring the breakage. The energy measurement arrangement may be arrangedto measure the energy applied directly to the rock particle during thebreakage, thus directly indicating the energy required to break the rockparticle. Some embodiments of the arrangement are described below.

Word “processor” is to be understood widely, it can be microprocessor(CPU), computer or some other suitable element, and it can be anintegral unit, or it can have several related but possibly detachedelements such as discrete components. The processor may be coupled to amemory that may be non-transitory such as a memory chip or a memorycircuit. The memory may store at least one computer program productcomprising a computer program code of instructions readable by theprocessor. The computer program code may then configure the processor toexecute a computer process for determining the breakage properties ofrock particles on the basis of the measurements described herein.

Processor PR includes, or has access to, data which contains therelationship of the measured feature (strain, speed) and the calculationoutput (compressive strength, breakage energy, and/or a degree ofbreakage of the rock particle).

Regarding the corresponding method, it is a method for testing breakageproperties of rock particles. The method comprises: weighing the rockparticles mass, inputting rock particles (one at a time) between twocounter-rotating crushing wheels 3, 3′ for crushing rock particles tosmaller daughter particles, accomplishing (performing, carrying out) aforce measurement for measuring information relating to the breakageforce applied to each rock particle RP, accomplishing (performing,carrying out) an energy measurement for measuring information relatingto energy absorbed by each rock particle (RP), calculating breakageforce applied to each rock particle (RP), and calculating energyabsorbed by each rock particle PR. The weight of the rock particles ismeasured with a suitable weighing device, and the weight value istransferred/inputted to the processor PR. In a case where there is afeeding mechanism for feeding the rock particles to the input gap, aweighing device may be arranged on the feeding mechanism such that therock particle is weighed before entering the input gap. The measuredweight is then electronically input from the weighing device to theprocessor.

In an embodiment, the energy measurement arrangement 5, 5′ is anarrangement for measuring the energy loss of the rotatable wheels 3, 3′during the breakage event of each rock particle RP. The crushing of rockparticle RP between the wheels 3, 3′ slows down the speed (androtational moment) of the wheels 3, 3′, and the amount of loss of speed(and loss of rotational moment) refers to the amount of energy loss,which in turn refers to the amount of energy given from counter-rotatingwheels to the rock particle RP. Regarding the corresponding method, inan embodiment, the method is such that energy loss of the rotatablewheels 3, 3′ during the breakage event of each rock particle ismeasured.

In a further embodiment, the energy measurement arrangement 5, 5comprises a sensor structure, said sensor structure being arranged tomeasure from the wheels 3, 3′ one or more of the following: speed,angular velocity, rotational position. Sensor structure may compriseoptical rotary encoder, having a hoop with a gear-like pattern of teeth,which are measured by an infrared optical gate of the type TCST-1103,mentioned as an example only. The sensor structure may then compute thereduction in the speed and/or angular velocity during the breakage, thusindicating the amount of energy transferred directly from the wheels 3,3′ to the rock particle during the breakage.

In the embodiment shown in FIG. 1, the motor is integrated directly tothe respective wheel. In a possible variation where the motor is notdirectly attached to the wheel, torque may be measured from theintermediate shaft. Torque may also be measured from reaction forces ortorque applied by the motor against the frame. The torque produced bythe motor signals energy transfer between the motor and the wheel, notdirectly between the wheel and the rock particle. In an embodiment, theenergy measurement arrangement is arranged to measure the energy appliedto the rock particle indirectly by observing the torque that the motorapplies to the wheel. The amount of torque measured depends on how themotor reacts to the loss of angular velocity of the wheel—in otherwords, how much torque for how many revolutions over what time isrequired to bring the wheel back to the starting speed.

Regarding breakage events, in a typical breakage event, there is a sharppeak of force when the rock particle enters the gap and touches bothwheels, followed by a short sustained plateau of force as the pieces ofthe rock are reduced further in size, and then a short taper off as theremaining pieces exit the gap. The highest forces measured are typicallyat the beginning of the breakage event with the initial breakage acrossthe whole cross-section area of the particle. This follows approximatelythe relationship of Stress=Force/Area, where the stress required tobreak the particle depends on the material (ideally), so the amount offorce required to break a particle or a fragment becomes less when thecross-section area of the particle or fragment of a particle becomessmaller. The smaller the gap is in relation to the original particlesize, the more the particle has to break down to fit through it. Thismeans more force must be sustained for a longer time, and more energy isspent.

In order to get more reliable measurement data from the forcemeasurement sensors 7, 7′ and/or from energy measurement sensors 5, 5′,in an embodiment to the test arrangement TA comprises of a controllerCNT for controlling the integrated gearless drive arrangement M1, M2,for disabling and/or limiting the drive arrangement M1, M2 regardingrotating the crushing rolls, in order to create interference-freeconditions for the measurement operations during breakage events. In anembodiment. the power supply to the motors M1, M2 is stopped to allowfree rotation. The motor will keep revolving with the roll (wheel). Anon-integrated drive configuration may also be mechanically separated bya mechanism, such as a clutch or a ratchet to remove the influence ofthe motor from the wheel. In any case, the crushing wheels 3, 3′ willkeep on rotating since the wheels 3, 3′ still have rotational kineticenergy. The energy measurement arrangement may then measure thereduction in the rotational kinetic energy of the wheels by measuringthe reduction in the angular velocity or speed of the wheels. Thereduction is a measure of the energy transferred from the wheels to therock particle during the breakage.

Regarding the corresponding method, in an embodiment, the method is suchthat drive arrangement M1, M2 of the wheels is disabled and/or limitedregarding rotating the crushing wheels, in order to createinterference-free conditions for the measurement operations duringbreakage events.

FIG. 2 shows the dependency of t₁₀ %-value and specific breakage EnergyEcs. A similar curve may be provided for other t_(x) %−values, e.g. t₅or t₂₀. In FIG. 2 horizontal axis represents a specific (=per unit ofmass) breakage energy Ecs shown in kWh/t (kilowatt-hour/ton). The curveshown in FIG. 2 is represented by the equation: t₁₀=A*(1−e^(−b*Ecs)),where ore specific parameters A and b are generated by least squaresfitting to the breakage test data represented by the measured degree ofbreakage (e.g. t₁₀ parameter) the measured energy, and the mass of therock particles under test. Parameters A and b differ for different orematerials and the Axb parameter is used to represent the resistance tobreakage, with lower values for more competent rocks. Ecs represents thespecific breakage energy and “e” is irrational and transcendental numberapproximately equal to 2.718281828459. Referring to FIGS. 1-2, in anembodiment, the test arrangement TA further comprises or allows (enablesconnection) use of a particle size analysis system SAS for measuring thesize of the daughter particles DP free-falling after being brokenbetween the crusher wheels (3, 3′), so as to determine the degree ofbreakage, e.g. particle size distribution (PSD) and/or the t₁₀ valuesThis t₁₀ value is the % passing 1/10 of the original size of theparticle, and the same analogy applies to the other t_(x) values.Alternatively, the degree of breakage such as the PSD and/or t_(x) canbe determined separately through mechanical sieving with a sieve havingselected properties. One example of the size analysis system SAS is anoptical detecting system such as a camera, coupled to the processor PR.

Referring to above, in an embodiment, the size analysis system SAS iscoupled to said processor PR, and said processor PR is arranged todetermine the correlation between the degree of breakage and measuredenergy absorbed by the rock particles RP. Regarding the correspondingmethod, in an embodiment the method is such that the method comprisesdetermining correlation between degree of breakage and measured energythe rock particles RP. FIG. 3 illustrates a method for determining thecorrelation between the energy and the degree of breakage, e.g. thecorrelation of FIG. 2.

Referring to FIG. 3, the test arrangement may be arranged to determinethe breakage-energy relationship of the tested material i.e. rockparticles RP, reference is made to FIG. 2, where horizontal axisrepresents specific (=per unit of mass) breakage energy shown in kWh/t(kilowatt-hour/ton). The specific breakage energy (kWh/t) is correlatedto the measured degree of breakage (e.g. the PSD or t₁₀) to determinethe rock breakage properties. A size specific energy (kWh/t of materialbelow a certain size) is calculated to determine a grindabilityparameter, while the force measurement is used to determine the rockmechanical properties (i.e. compressive strength). Accordingly, twoindependent measurements for determining different properties may becarried out concurrently. Regarding the corresponding method, in anembodiment the method is such that breakage-energy relationship of therock particles (RP) is determined in the method. Following FIG. 3, themethod may comprise the following steps or operations. In block 300, themass of the rock particles is measured, e.g. by using a weighing devicedescribed above. The measured mass per rock particle may be stored in amemory accessible to the processor. In block 302, each rock particle isfed into the input gap for breakage, and the rock particles are brokenbetween the wheels while the wheels are rotated by the motor. Theprocessor may control the drive arrangement to start rotating the wheels3, 3′ and, in some embodiments, disable the drive arrangement justbefore the breakage of each rock particle. The processor may alsoconfigure the energy measurement arrangement to start the measurement.

During the breakage, the energy and force measurement arrangementsmeasure the breakage energy and force, e.g. in the above-describedmanner. The measured breakage energy absorbed per rock particle isstored in the memory accessible to the processor. Upon measuring themass and the breakage energy, the processor computes the specific energyper rock particle (block 308). In block 312, the particle sizedistribution (PSD) or degree of breakage (t10) are measured for thebroken rock particles. The degree of breakage may be measuredautomatically by the SAS, or it may be measured manually, e.g. by usinga sieve. The measured degree of breakage may comprise the full PSDand/or a t_(x) parameter such as the t₁₀ parameter. The PSD and/ordegree of breakage is measured for a set (i.e. sample) of rock particlesand stored in the memory. In summary, the memory may store, for eachrock particle, a record comprising the mass, breakage energy and force,as well as the degree of breakage of the population of rock particle.Upon computing the specific energy and the degree of breakage for therock particles, the correlation between the two parameters may be builtin block 314 by the processor. The correlation may include performing aregression analysis or fitting for the sample set where each samplecomprises a pair of a degree of breakage and a corresponding specificenergy (the samples of FIG. 2). The correlation function or acorrelation curve may then be output by the processor, e.g. for furtheranalysis of the rock material or for designing comminution systems. Theoutput may be via a user interface coupled to the processor or via acommunication network adapter.

In an embodiment, the procedure of FIG. 3 is also used to compute agrindability parameter such as a bond ball mill work index (BBMWi). Onthe basis of the specific energy Ecs, a size-specific energy may becomputed. The size-specific energy may be defined as

Mean(Ecs)/%−X

where %−X is the cumulative percentage of particles passing a chosensieve of aperture size X (measured after the breakage, naturally). Theaperture of the sieve (X) may be defined in terms of microns, e.g. 150microns, 270 microns, or any other size. For example, if the meanspecific energy measured from the breakage of multiple rock particles(e.g. 20 particles or 50 particles) is 1 kWh/t and the cum%pass is 10%for a 150 micron sieve (10% of broken rock particles pass the sieve),the size-specific energy is 10 kWh/(t of −150 microns). Thesize-specific energy may then be mapped to the grindability parameterBBMWi value by using a correlation table stored in the memory. Thecorrelation table may be built via empirical measurements and, in thecontext of the present embodiment, the mapping table is readilyprovided.

In an embodiment, the test arrangement TA is arranged to determine thecompressive strength of the tested material (rock particles RP). Formeasuring the compressive strength, the force measurement arrangementmay be used. In block 306 of FIG. 3, the breakage force is measured perrock particle and stored in the memory. FIG. 4 illustrates a forcemeasurement signal where the peak force represents an impact of the rockparticle being crushed between the wheels, and this peak force may bemeasured and stored. In some embodiments, not only the peak but also thesamples representing the slopes of the peak and/or force measured afterthe peak may be stored in the memory. Thus measured breakage force(s)may then be used by the processor when computing a mechanical propertyproxy parameters such as an unconfined compressive strength (UCS) or apoint load strength index (PLTi) of the rock particles. Both of theseparameters represent compressive strength of the rock particles and areas such known to the person skilled in the art of rock mechanics. Theseproxy parameters may be provided on different scales that are adapted toa particular test method, e.g. the unconfined compressive strength testor a point load test. In block 310, The mapping between the force(s)measured in block 306 and the respective grindability parameters may bestored in the memory and built via experimentation with the particulartest arrangement described herein.

It will be obvious to a person skilled in the art that, as thetechnology advances, the inventive concept can be implemented in variousways. The invention and its embodiments are not limited to the examplesdescribed above but may vary within the scope of the claims.

1-15. (canceled)
 16. Test arrangement for testing breakage andmechanical properties of rock particles, said test arrangementcomprising: a support; two counter-rotatable crushing wheels supportedon the support; a drive arrangement for rotating the crushing wheels,said crushing wheels facing each other and defining therebetween aninput gap for the rock particles, said wheels being arranged to breakthe rock particles to smaller daughter particles; wherein the testarrangement is arranged to receive only one rock particle at a time tobe inputted to the input gap for breakage testing; an energy measurementarrangement arranged to measure information relating to energy absorbedby the rock particles during the breakage; and a processor coupled tothe energy measurement arrangement and arranged to receive, as inputs,at least one degree of breakage of the rock particles as a result of thebreakage and the corresponding breakage energies absorbed by the rockparticles during the breakage, to determine a correlation between thedegree of breakage and the breakage energies, and to output thecorrelation.
 17. Test arrangement according to claim 16, wherein theenergy measurement arrangement is an arrangement for measuring theenergy loss of the rotatable wheels during the breakage event of eachrock particle.
 18. Test arrangement according to claim 17, wherein theenergy measurement arrangement comprises a sensor structure, said sensorstructure being arranged to measure speed and/or angular rotationalposition of the wheels.
 19. Test arrangement according to claim 16,wherein the test arrangement comprises a controller for controlling thedrive arrangement, for at least one of disabling and limiting the drivearrangement regarding rotating the crushing wheels, in order to createinterference free conditions for the measurement operations duringbreakage events.
 20. The test arrangement according to claim 16, whereinthe degree of breakage comprises a t10−value representing %−value ofmaterial passing 1/10th of the original particle size.
 21. The testarrangement according to claim 16, further comprising a feederconfigured to feed the rock particles to the input gap such that onlyone rack particle at a time is input to the input gap.
 22. The testarrangement according to claim 16, wherein the processor is configuredto receive, as a further input, a mass of each rock particle before therock particle is input to the input gap, to compute a specific breakageenergy for each rock particle on the basis of the mass and the measuredbreakage energy
 23. The test arrangement according to claim 16, whereinthe drive arrangement comprises a gearless motor.
 24. The testarrangement according to claim 16, further comprising the processor isconfigured to compute at least one size specific energy and at least onegrindability parameter on the basis of a stored correlation between theat least one grindability parameter and the size-specific energy. 25.The test arrangement according to claim 16, further comprising a forcemeasurement arrangement arranged to determine compressive strength ofeach of the rock particles during the breakage, wherein the processor iscoupled to the force measurement arrangement and configured to receive,as a further input, the compressive strength and to compute at least oneparameter representing compressive strength of the rock particles. 26.Method for testing breakage properties of rock particles, comprising:weighing the rock particles' mass; inputting the rock particles betweentwo counter rotating crushing wheels to break the rock particles tosmaller daughter particles such that said rock particles are inputbetween the crushing wheels one at a time for said breakage;accomplishing an energy measurement for measuring information relatingto energy absorbed by each rock particle; determining at least onedegree of breakage of the rock particles resulting from the breakage;calculating, by a processor on the basis of the degree of breakage andthe corresponding breakage energies measured by the energy measurement acorrelation between the degree of breakage and the breakage energies,and outputting, by the processor, the correlation.
 27. The methodaccording to claim 26, wherein the energy measurement is measured energyloss of the rotatable wheels during the breakage event of the rockparticles.
 28. The method according to claim 26, wherein said weighingis performed by a scale coupled to the processor.
 29. The methodaccording to claim 26, further comprising: accomplishing a forcemeasurement to determine compressive strength of each of the rockparticles during the breakage, computing, by the processor on the basisof the force measurement, at least one parameter representingcompressive strength of the rock particles.
 30. The method according toclaim 26, wherein the drive arrangement of the wheels is disabled and/orlimited regarding rotating the crushing wheels during the breakage, inorder to create interference free conditions for the measurementoperations during the breakage.
 31. The method according to claim 26,wherein the processor computes a specific breakage energy for each rockparticle on the basis of the mass and the measured breakage energy ofsaid each rock particle, and further computes a grindability parameteron the basis of the specific breakage energy.